The invention concerns generally the technology of allocating resources for individual radio connections at the interface between a transmitting device and a receiving device. Especially the invention concerns the allocation of radio resources for a packet-switched radio connection which is a continuation of a previous connection of essentially the same type.
Multi-user radio communication systems must have well-defined procedures for allocating radio resources (time, frequency) to individual radio connections. In this patent application we will consider especially packet-switched radio connections in cellular radio systems where each cell comprises a base station which is arranged to communicate with a multitude of mobile stations. As an example we will discuss the well-known GPRS system (General Packet Radio Service), the known resource allocation procedures of which are laid down in the technical specification number GSM 04.60 published by ETSI (European Telecommunications Standards Institute). The acronym GSM refers to the known Global System for Mobile telecommunications. We will briefly describe some parts of said specification in the following.
The concept of Temporary Block Flow or TBF has been introduced to facilitate the unidirectional transfer of data between a base station and a mobile station. According to its definition, a TBF is a physical connection used by two mutually communicating RR (Radio Resource) entities to support the unidirectional transfer of the Protocol Data Units or PDUs from upper (LLC; Logical Link Control) layers on physical channels for packet data. We will consider separately uplink TBFs (transfer of data from the mobile station to the base station) and downlink TBFs (transfer of data from the base station to the mobile station), starting with the first of these.
During an uplink TBF the mobile station will organise the data to be transferred into Protocol Data Units or PDUs. These are in turn divided into smaller parts which are distributed into RLC data blocks, where RLC comes from Radio Link Control which is one of the layers in the protocol stack which defines the procedures related to information transfer over the radio interface. Each RLC data block will have a corresponding identification number as well as a multitude of associated fields containing information that relates to the contents and significance of the RLC data block. One of said fields contains a so-called Countdown Value or CV which is a non-negative integer number less than or equal to 15. A value 15 in the CV field indicates that there are so many remaining RLC data blocks to be transmitted during the present uplink TBF that their number, scaled by the number of timeslots assigned to the uplink TBF, is greater than the value of a certain broadcast parameter BS_CV_MAX. All smaller values in the CV field indicate that there are exactly that many remaining RLC data blocks, scaled by the number of timeslots assigned to the uplink TBF, to be transmitted.
Fig. 1 illustrates the procedures relating to the end of an uplink TBF, with time running from top to down. At step 101 the mobile station MS transmits to the base station BS (or more generally: to the network) an RLC data block with a CV value 0, indicating that there are no remaining RLC blocks to be transmitted. Having successfully received the last RLC block and detected it as such, the base station (or network) transmits to the mobile station an acknowledgement message at step 102 with a certain Final Ack Indicator or FAI indicating that no further retransmissions of RLC data blocks are required. The same acknowledgement message will contain a valid RRBP (Relative Reserved Block Period) field assigning to the mobile station one uplink sending permission which the mobile station will use to transmit at step a Packet Control Acknowledgement message indicating that the final acknowledgement from the base station has come through. After having received the last-mentioned message the network is free to re-allocate the resources previously reserved for the discussed TBF to some other purposes.
The concept of Block Periods is associated with the fact that in GPRS the capacity of a Packet Data Channel or PDCH can be shared by many TBFs and so the network allocates packet data resources for the mobile stations in the units of an RLC block period.
During a downlink TBF a similar arrangement of successive RLC data blocks is produced by the network and transmitted to the mobile station. A CV field is not present in the downlink RLC data blocks, but there is a so-called FBI or Final Block Indicator bit which is used to mark the last RLC data block. In FIG. 2, step 201 corresponds to the network transmitting to the mobile station an RLC data block with FBI value xe2x80x981xe2x80x99. Taken that there were no previous unsuccessfully transmitted RLC data blocks that would require retransmission, the mobile station answers with an acknowledgement message at step 202 with a Final Ack Indicator or FAI indicating that no further retransmissions of RLC data blocks are required (if retransmissions would have been required, a number of retransmission requests and retransmissions would come in between steps 201 and 202). Simultaneously it starts a timer of predetermined duration which is illustrated in FIG. 2 as the hatched bar 203. While the timer is running the mobile station continues to monitor the Packet Data Channels or PDCHs which were assigned to the TBF. If the mobile station receives on a monitored channel another RLC data block with the FBI set to xe2x80x981xe2x80x99 while the timer is running, it will retransmit the final acknowledgement message. After the timer has expired, the mobile station will consider the TBF as released, abort the monitoring of the assigned Packet Data Channels and return to a state in which it monitors one or more common control channels.
The problems of the described terminating procedures for uplink and downlink TBFs (or, more generally, packet-switched radio data connections) arise from the occasional need for continuing a connection for which the termination procedures have already been initated. It may happen that the application that produces the information to be transmitted reactivates with a short notice, or an additional burst of information to be transmitted emerges for some other reason. Let us briefly describe what happens according to the known features of GPRS.
In an uplink connection, the mobile station is not allowed to increment the value of the CV field if it is already less than 15, even if it suddenly finds out that there are actually more RLC data blocks to be transmitted than what the value in the CV field would suggest. According to the known specifications the terminating TBF must be completely exhausted, i.e. the value of the CV field must decrease monotonously until the mobile station and the base station have gone through the procedures described above with reference to FIG. 1. For the new data the mobile station must request a completely new allocation of radio resources by first transmitting a request message on an access channel (PRACH or RACH; Packet Random Access Channel or Random Access Channel depending on whether or not the first one of these is available). The network will either grant or reject the request by sending a corresponding message on an access grant channel (PAGCH or AGCH; Packet Access Grant Channel or Access Grant Channel, same considerations of availability apply). The access-request-and-grant procedure may take several seconds which causes unnecessary delay to the transmission of information. It also causes a considerable amount of signalling traffic and may give rise to collisions with other simultaneous access requests from other mobile stations in the same cell.
In the downlink direction the network may send to the mobile station a Packet Downlink Assignment on a PACCH (Packet Associated Control Channel) which the mobile station is monitoring while the termination timer referred to above is running, but the mobile station will interprete such an assignment as a resource reassignment. In other words the mobile station will change to the new time/frequency combination defined in the assignment and continue the downlink TBF release procedure there although the network has successive PDUs to be transmitted. The mobile station will thus listen the allocated PDCHs until the termination timer expires after which it will consired the TBF as released, abort the monitoring of the assigned PDCHs and return to a state in which it monitors one or more common control channels. Also it may happen that the network should transmit successive PDUs which require a different RLC mode. To change RLC modes the network must allow for the termination timer in the mobile station to expire and establish a completely new TBF by sending a Packet Downlink Assignment message on a PCCCH or CCCH (Packet Common Control Channel or Common Control Channel depending on availability).
From the technology of circuit-switched radio telephone connections there is known a method for providing a terminal device with a certain amount of reserved radio resources after the termination of a connection. The U.S. Pat. No. 5,574,774 describes a system in which certain subscribers of a mobile telephone network may enjoy a privileged service so that after the privileged subscriber has taken part in a telephone connection and the other party of that connection has terminated the call, the privileged subscriber still has at his disposal the resources that were allocated to the call for a certain duration of time. The reason for keeping the resources reserved is to guarantee for the privileged subscriber the right to make another call even if there is congestion in the network. The party that will benefit the most from such an arrangement is the mobile telephone operator, because from the network point of view keeping the resources reserved corresponds to conducting an active telephone call and is charged for accordingly; for those cases in which the privileged subsciber is not interested in using his priority rights he will end up paying for nothing.
It is an object of the present invention to provide a method, a mobile station and a network device for enabling a fluent continuation from an old packet-switched communication connection to a new one. It is also an object of the invention that it will require only a moderate amount of signalling over the radio interface.
The objects of the invention are achieved by incorporating into the terminating procedures of a packet-switched communication connection a certain message through which the transmitting device may inform the receiving device about its need to continue the transfer of information.
It is characteristic to the method according to the invention that it comprises, in the following order, the steps of
indicating the termination of a terminating communication connection through a communication resource associated to the terminating communication connection and
indicating the need for a continued communication connection through a dedicated communication resource.
The invention applies also to a mobile station comprising as its characteristic features the means for
indicating the termination of a terminating uplink communication connection through a communication resource associated to the terminating communication connection and
indicating the need for a continued uplink communication connection through a dedicated communication resource.
Additionally the invention applies to a base station subsystem characterised in that it comprises means for
indicating the termination of a terminating downlink communication connection through a communication resource associated to the terminating communication connection and
indicating the need for a continued downlink communication connection through a dedicated communication resource.
We will continue considering the uplink and downlink cases separately because of their slightly differing characteristics. In the uplink case it is on the responsibility of the mobile station to indicate to the network that the packet-switched connection should continue. This will require a corresponding message to be transmitted in the uplink direction from the mobile station to the base station. According to the invention, instead of just acknowledging the final message sent by the network and indicating the succesful reception of the last uplink part of the terminating connection, the mobile station will use the available responding resources to make said indication. The network has then the choice to either reject or accept the indication. In the case of acceptance, a new (or continued) connection will be set up without the need for the mobile station to go through the previously inevitable time-consuming access request round on a random access channel that is common to all mobile stations.
In the downlink case it is the network that has to indicate to the mobile station the suddenly occurred need to continue transmitting data on a dedicated channel. According to the invention the network will exploit the time during which the mobile terminal is still monitoring the previously allocated dedicated channels and transmit an assignment message. In order to avoid the simple resource reassignment interpretation referred to above in the description of prior art, the network will introduce into the assignment a specific field the value of which tells the mobile station to interpret the assignment differently. This way it is possible to even completely reconfigure the packet-switched connection before continuing the transmission of data, and still the use of a common control channel is avoided.